build(docs-infra): remove todo and skipLibCheck left behind from typescript 5…

[arjenbrandenburgh]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/main/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.io application / infrastructure changes
• Other... Please describe:

What is the current behavior?

The adev/tsconfig.json file in the Angular development setup currently has the TypeScript compiler option skipLibCheck set to true. This setting, a temporary measure noted for accommodating TypeScript version 5.4 support, disables type-checking for declaration files of installed libraries. This was done in #54414.

What is the new behavior?

This PR reverses the temporary disabling of library type checks ("skipLibCheck": true) in adev/tsconfig.json. Re-enabling these checks ensures stricter type safety during TypeScript compilation, enhancing Angular's code quality and stability.

Does this PR introduce a breaking change?

• Yes
• No

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[JoostK]

Although the change LGTM, this should not be fix(core) since it's not affecting core. build(docs-infra) seems more appropriate.

[arjenbrandenburgh]

Hey fellow Utrechter, you're absolutely right. I did find it challenging to pinpoint the exact right tag for this one. Thanks for pointing out that build(docs-infra) would be a more fitting choice given the context of the change since it entails a tsconfig file.

[crisbeto]

Let's wait and see, but I think that this will fail the release check since the Angular version for adev would have to be set to 17.3 first. I think that would happen in another repo.

[alan-agius4]

Note for context in the Angular CLI we removed this from users projects due to TypeScript recommending this. https://www.typescriptlang.org/tsconfig#skipLibCheck